This invention relates, in general, to microprocessors and sensors and more particularly, to a microprocessor having an integrated environmental sensor which is process compatible with microprocessor technology.
A wide variety of solid state sensor devices are available which produce electrical output in response to environmental conditions. The sensors can be broken generally into several basic categories: mechanical sensors, temperature sensors, magnetic field sensors, optical sensors, and chemical sensors. Sensor devices are often identified by a particular application such as biomedical sensor and gas sensors, but these generally fit into one or more of the basic categories.
Solid state sensors are generally analog devices, and as such their output is sensitive to a variety of ambient conditions. This property is advantageous in detecting an environmental condition, i.e. detecting pressure for a pressure sensor, but detrimental in that a pressure sensor is also sensitive to temperature, light, and package stress. These other sensitivities create noise signals in the output which must be filtered or compensated.
Recently, integrated sensors have become available with both passive and active compensation circuits built on the same chip as the sensor device. Examples of such devices in pressure sensors are found in U.S. Pat. No. 4,463,274 and U.S. Pat. No. 4,465,075 issued to Craig C. Swartz. Such devices are useful in providing some preconditioning to the sensor output before the output signal is passed to the other circuitry.
Another recent development is the increasing application of microprocessors (MPUs) and microcontrollers. Microprocessors have been used with sensor devices to process and control the sensor output. MPUs can be used to calibrate and compensate sensor output, as well as active filtering of sensor output. Microprocessors having high current drive are also known which can be used to control motors, compressors, pumps and the like.
In the past, sensors and MPUs have been physically located away from each other, and not manufactured on the same monolithic substrate. This is because sensors are exposed to the environment which is to be sensed while conventional wisdom dictates that the MPU be removed from this environment. The environment to which a sensor is exposed is often extremely harsh. Likewise, MPUs, especially when combined with power devices, create noise which affect sensor devices. In particular, heat generated by MPUs and power devices has led the industry away from mounting sensors near MPUs.
The physical separation of the MPU from the sensed environment created constraints which curbed sensor utility. Physical separation creates larger systems which are more obtrusive to the environment to be sensed, and which were too large to be located in many environments. Also, separation makes it necessary to either port the environmental signal to the sensor-microprocessor system or port an electrical signal from a discrete sensor to the microprocessor. Either of these options is particularly sensitive to noise, and reduces system performance.
Although MPUs and sensors are both solid state devices, their differences in construction and operation have led the semiconductor industry to shun their integration. Pressure sensors and accelerometers, for example, required delicate micro-machining and carefully controlled processing which has not been compatible with CMOS MPU devices. Micro-machining involves silicon etching which weakens silicon substrates and increases breakage during processing. CMOS MPUs, on the other hand, are complex devices which are too expensive to risk breakage. In the case of non-mechanical sensors, the MPU is adversely affected by exposure to the environmental signal such as light, a magnetic field, or chemical exposure. Until now, MPUs have not been designed to operate in these environments.
In operation, most sensors generate analog signals which have been difficult to process in digital microprocessors. Interface circuits used to couple the analog sensor signal to an MPU required additional semiconductor devices and further discouraged monolithic integration of sensors and microprocessors. The fact that MPU designers have little familiarity with sensor design and vice versa has also slowed progress and limited recognition of the need for integrated MPUs and sensors, and the particular problems associated with their integration.
Accordingly, it is an object of the present invention to provide a solid state sensor monolithically integrated with a microprocessor.
Another object of the present invention is to provide a means for isolating the microprocessor from an environmental signal to which the sensor is exposed.
A further object of the present invention is to provide a sensor having an integrated microprocessor wherein the sensor incorporates a similar process as the microprocessor.
A still further object of the present invention is to provide a high power output sensor device with integrated data processing capability that can drive a load.